21 week old rolling around cot!

my little girl has been a great sleeper up until 2 weeks ago. now she wakes a lot. she rolls over onto her tummy & crawls up to the top of the crib and doesn't sleep like she used to. we have to constantly get up and turn her over onto her back as she gets frustrated on her belly. we just had to give her her soother throughout the night previously but now she is awake a lot more wriggling around. she goes to bed at 8 pm and gets up at around 8.30am..